This invention relates to a propulsion system and method for air vehicles, and more particularly, to a propulsion system and method for aircraft having rocket engines, scram jet engines or ram jet engines. Liquid hydrogen, liquid hydrocarbon and liquid oxygen are stored and used in a systematic way to achieve the necessary requirements of high propulsion thrust, low air vehicle weight and low air vehicle drag in a relatively simple air vehicle and propulsion system design.
Single-stage-to-orbit flight can be considered from the standpoint of high acceleration rates resulting from a combination of high net available thrust, low weight of the air vehicle and low aerodynamic drag. The weight of the propellants diminishes as flight progresses, and with positive net thrust available, the air vehicle will reach orbital insertion velocity at orbital altitudes as long as propellant reserves are available. Therefore, a key factor in propulsion of air vehicles is the amount of propellant relative to air vehicle size. A second key factor in single-stage-to-orbit flight is low fixed weight of the air vehicle and the propulsion system since this weight must be countered by thrust during the entire ascent to orbit. A third factor in single-stage-to-orbit flight is the shape of the air vehicle which must yield a favorable relationship of lift and drag. The final key factor is high thrust from the propulsion system, namely, the rocket engines of the air vehicle. In view of the foregoing, it can be easily seen that it is desirable to increase the amount of propellant relative to the size of the air vehicle; to reduce the fixed weight of the air vehicle and propulsion system, thereby reducing the amount of thrust to propel the air vehicle and propulsion system to orbit; to improve the aerodynamic shape of the aircraft; and to improve the amount of thrust which can be achieved by the propulsion system.
A large number of liquid propulsion systems including multiple-propellant liquid propulsion systems, are currently known in the art. However, it is difficult to store the propellants in the air vehicle to achieve maximum utilization of storage space in the vehicle while reducing the weight of the storage tanks and providing an air vehicle having low aerodynamic drag. In order to achieve the foregoing for liquid propellant propulsion systems, it has generally been necessary to provide vacuum-type storage tanks in air vehicles to store liquid propellants. Vacuum-type storage vessels and systems are difficult to maintain and substantially increase the weight of the air vehicle. Accordingly, it is desirable to eliminate the requirement of vacuum-type storage tanks and other bulky systems for the storage of liquid propellants on board air vehicles.
Hydrocarbon-liquid oxygen mixtures have been widely used as propellants in propulsion systems of air vehicles. It is known that such hydrocarbon fuels burn in combustion chambers at temperatures exceeding 5000.degree. F. and generate a great amount of thrust. However, propulsion systems for more recent air vehicle design require greater thrust than that which is generally achieved by the hydrocarbon-liquid oxygen mixtures, and generally, more complex propellants in more complex propulsions systems have been developed to provide higher thrust. Most of these complex propellants cannot be used in conventional propulsion systems for various reasons, such as extremely high combustion temperatures, and complex propulsion systems and storage systems must be developed to accommodate the burning of such propellants. The complex propulsion systems which overcome these difficulties contribute substantially to the weight of the air vehicle. In view of the foregoing, it can been seen that it would be advantageous to utilize the less complex propulsion systems based on hydrocarbon-liquid oxygen fuel mixtures to overcome the foregoing disadvantages.
It is well known that certain chemical substances such as high molecular weight hydrocarbons, react endothermically to produce reaction products which can be used as fuel. Prior art systems have been developed which convert certain chemical substances by endothermic reactions into fuels which can be burned in a combustor. However, many of the prior art systems are disadvantageous because the process of endothermic reaction produces certain reaction products which can build up an undesirable coating in the combustor. Accordingly, it is desirable to provide a propulsion system which utilizes the simple hydrocarbons, such as, ethylene, ethane, propylene and propane, as the chemical substance which endothermically reacts to produce predominantly only reaction products useful as improved fuels in propulsion systems of air vehicles.
In prior art propulsion systems which utilize fuels which produce high temperatures in the propulsion system, such as, in a combustion chamber, it has been difficult find materials which can withstand the high temperatures, that is, temperatures of 5000.degree. F. and higher. Many types of combustor liners and throat liners of rocket casings have been proposed, however, they are complex and expensive or have limited lifetime or require excessive amounts of coolants circulated therethrough to prevent structural weakening and/or melting of the liner material. Accordingly, it is desirable to provide improved combustor and throat designs and materials in propulsion systems which overcome the foregoing disadvantages.